One of Wall St's biggest bulls throws in the towel

For years, Piper Jaffray has been one of the biggest bulls on Wall Street, and with good reason.

This week, though, amid market carnage not seen since the financial crisis, the firm has decided it's seen enough.

Piper finally slashed its uber-optimistic market call for 2015, cutting its S&P 500 price target from what now seems an unreachable 2,350 all the way down to 2,135.

"We no longer believe the odds are in our favor for the S&P 500 to reach our prior target of 2,350 by year-end, since history shows that recoveries from pullbacks/corrections have generally taken about two to four months to materialize," Craig Johnson, technical market strategist, said in a note.

The call comes as traders prepare for yet another day of carnage that could see the market's biggest drop since the darkest days of the financial crisis in 2008. Fears of a China slowdown turning into a global recession have caused a market tumble that could put an end to a six-year bull market.

The Dow industrials are in a full correction mode, dropping more than 10 percent from their highs, while multiple S&P 500 sectors are there as well.

Key support levels ahead for the latter index are 1,905, a 3 percent drop from Friday's close, and then 1,820, a violation of which "would alter the longer-term uptrend of the broader market."